1. Field of the Invention
The invention is situated in the area of the further processing of printed products and concerns a method and device in accordance with the generic parts of the corresponding, independent claims. Method and device serve the production and strapping of recumbent stacks of printed products.
2. Description of the Related Art
In the printing industry, intermediate and part products, such as individual sections of newspapers and periodicals being printed prior to other sections, signatures to be made into books, or single sheets, prospectuses, small brochures, part sheets, etc. to be inserted into newspapers or periodicals as supplements or as collated parts, require intermediate storage between production and further processing and therefore must be transported within the company or, if necessary, from one company to another. For such intermediate storage and transportation it has long proven advantageous to arrange the intermediate products in recumbent stacks, so called bars, and e.g. to store and transport these, stacked on pallets.
Usually the length (perpendicular to the flat surface of the printed products) of these aforementioned stacks is substantially greater than the length of the edges of the printed products. This means that such stacks are unstable without aid, even in an upright position. The length of the stacks corresponds e.g. with the measurements of the pallets on which they are stacked to be stored and transported, i.e. the stacks normally measure 120 or 150 cm in length and may contain e.g. 200 to 300 printed products. The stacks are laid on to the pallets and stacked on top of each other, forming storage units which are easily and compactly handled with commonly used warehouse vehicles.
The ends of the stacks are usually stabilized by endplates, e.g. wooden plates which correspond in size to the stacked products, and the stacks are held together in a compressed condition by a strap, e.g. consisting of a plastic tape. The strap runs across the longer edge of rectangular products; depending on the format of the product, once in the middle, or twice dividing the stack face into three about equal parts.
The recumbent stacks are usually produced by lining up products standing on one edge, by stabilizing the lined-up products at either end with endplates, and by subsequent compression and strapping. The printed products to be processed into such stacks are therefore e.g. supplied in a stream of printed products overlapping each other (imbricated stream) from above on to a horizontal, or slightly sloping, conveying surface and are positioned thereon. Standing one behind the other on one edge (usually folding edge or back edge) and supporting each other on the conveying surface, they are conveyed or pushed away from the supply point. Thus a recumbent stack is formed on the conveying surface which stack grows continuously in the stacking direction (conveying direction of the conveying surface). From this continuously growing stack, discreet stacks of a pre-determined length or number of products are successively isolated, fitted with endplates on both ends, compressed and strapped. The endplates are usually positioned during stack growth in corresponding gaps of the growing stack. In order to be strapped, the isolated stacks, fitted with endplates, are accelerated in stacking direction and conveyed into a strapping position. After strapping the stacks are conveyed away.
A device for the formation and strapping of recumbent stacks of printed products, as described briefly above, is e.g. known from the publication U.S. Pat. No. 4,772,003 (Nobuta et al.). In this device an imbricated stream is supplied from above on to a slightly sloping conveying surface. The supply is periodically interrupted such that discreet stacks are produced straight away. In order to support the stacks being formed on the conveying surface, to position the endplates, and to forward the complete stack in the stacking direction, intermittently activated elements are used; three of which reaching into the area of the stack from below the conveying surface and one from above. To be compressed and strapped, the forwarded complete stack is pushed transverse to the stacking direction into a compression and strapping station, its faces being supported by stationary supports.
A further device for producing and strapping recumbent stacks of printed products is known from the publication EP-0623542 (Grapha-Holding AG). In this device an imbricated stream is continuously supplied on to the conveying surface, creating a continuously growing stack. To intercept the continuously growing stack a four-part dividing element is inserted into the stack at the supply point, is conveyed with the growing stack in the stacking direction, and is then straddled to create a gap. Halves of a downstream and an upstream compression jaw, which also position the endplates, are inserted into the gap from either side of the stack. The compression jaws take over the stack from the components of the four-part dividing element and forward it in stacking direction to be compressed and strapped. The compression jaws are arranged on a guide system above the conveying surface, which enables them to move back and forth parallel to the stacking direction. In addition, the halves of the compression jaws can be moved transverse to the stacking direction in and out of the stack area. A stationary looping channel is provided in the strapping position. For strapping, strapping material positioned in the looping channel is extracted to be placed around the stack and is then tightened. The looping channel comprises two vertical components, one on the entry side and one on the exit side of the strapping position, and a horizontal component which connects the vertical components by reaching lengthwise across a stack to be strapped. The horizontal channel component is arranged in such a way that it lies between the two halves of the compression jaws which convey the stack into the strapping position. For this conveyance the entry side vertical channel component is lowered below the conveying surface. This means that the loop of the strapping material cannot be placed in the looping channel until the stack is positioned in the strapping position and the vertical channel component has been repositioned in its active position above the conveying surface.